The present invention generally relates to a hydraulically-assisted automatic shifting method and associated apparatus in accordance and, more particularly, to a method for the hydraulically-assisted automatic shifting of a multi-path toothed-wheel gear change box with a gearbox arrangement in which an input shaft can be brought into driving connection with an output shaft via at least on of at least two gearbox subunits arranged in parallel to one another in a force flux, one power-shift clutch is arranged in the force flux between the input shaft and in each case one gearbox subunit, at least one of the gearbox subunits has at least two gearwheel stages with in each case one loose wheel which can be coupled to its shaft by a positively engaging gearwheel clutch, and the transmission ratios of the gearwheel stages are configured such that, in each case in relation to two gears adjacent in terms of their transmission ratio, in one gear one associated gearbox subunit: and, in the adjacent gear, another gearbox subunit associated with the latter is connected into the driving connection by subjecting in each case one clutch actuator actuating the associated power-shift clutch to working pressure.
In a known shifting method, as shown in VDI Report No. 672, 1988, page 383, with a gearbox arrangement having two gearbox subunits, it is regarded as disadvantageous that shifts without an interruption to the tractive force are only possible between two gears in which the flux of force does not take place via one and the same gearbox subunit and a crossover control for the power-shift clutches ca consequently be effected. For this reason, skipping gears has only been considered to be possible over two gears.
EP 0 273 735 A2 discloses a method for electronic control of a toothed-wheel gear change box which is connected downstream in an engine flux of force, via a power-shift clutch and in which an optimum gear is selected as a function of shift characteristics which take account of driving speed and accelerator-pedal position. When a shift command for an upshift via two or more gears is issued, a shift is first effected into the next-highest gear for a predetermined period of time, during which the upshift of the shift command is suppressed.
DE 34 06 218 A1 discloses a method for hydraulically assisted automatic downshifting from the fourth gear to the second gear of a multi-path planetary gear change box with a gearbox arrangement in which, in fourth gear, an input shaft can be brought into driving connection with an output shaft via a first, simple planetary gearbox subunit by engaging a first frictional shifting clutch situated between the input shaft and this gearbox subunit in the flux of force. In second gear, it is brought into driving connection with the input shaft additionally via a second simple planetary gearbox subunit by a direct connection between the input shaft and the inner sun gear of the second gearbox subunit and by engaging a second frictional shifting clutch connected to the planet carrier of the first gearbox subunit and to the outer sun gear of the second gearbox unit. In the intermediate third gear, the input shaft and the output shaft are coupled to one another by engaging both shifting clutches via the two gearbox subunits which, as a result, revolve as a block. During the shift from fourth to second, a restriction device comes into effect which retards the engagement of the second shifting clutch relative to its engagement during the shift from fourth to third.
An underlying object of the present invention consists essentially in providing a shifting method in which a shift is made possible without an interruption to the tractive force, between two gears which, in terms of their transmission ratio, are nonadjacent and for which one and the same gearbox subunit is connected into the driving connection between the input shaft and the output shaft. Consequently, in a gearbox arrangement having, for example, only two gearbox subunits, only a single gear is skipped (shifts via two gears).
The foregoing object has been explained is achieved in an advantageous manner by utilizing a shifting method and associated apparatus in which the purpose of changing over between two nonadjacent gears, in each case another associated gearwheel stage of the sam gearbox subunit is connected into the driving connection, a middle gear which lies between the two nonadjacent gears in its transmission ratio and in which a gearwheel stage of another gearbox subunit is connected into the driving connection and temporarily engaged, and the working pressure in the clutch actuators of the power-shift clutches of the two gearbox subunits taking part in the changeover is controlled in such that the characteristic of the speed of the input shaft between the speed value corresponding to the old gear and the speed value corresponding to the new gear is at least approximately steady, without remaining at the speed value of the middle gear.
In the method of the present invention, unpleasant torque fluctuations at the output shaft are largely avoided because, on one hand, a direct jump of the torque between the torque values associated with the two nonadjacent gears is avoided and, on the other hand, the torque in the middle gear which is engaged and disengaged transitorily, in each case by a crossover control i.e. without interruption to the tractive force is adjusted to a torque value by the working pressure for the actuation of the power-shift clutch associated with this gear such that a low-jerk transmission between this torque value and the two torque values of the nonadjacent gears is in each case obtained.
The method of the present invention can be used both for upshifts and for downshifts. For upshifts, the clutch torque in the middle gear in the sense according to the invention is held above the value associated with this middle gear whereas, for downshifts, the clutch torque is held correspondingly below the value associated with the middle gear.
In the event of a downshift via two gears which are nonadjacent in terms of their transmission ratio in the method according to the present invention, it is ensured that, in a first shifting phase, the engine can increase its revs by virtue of a reduction in the working pressure, i.e. the speed of the input shaft rises steadily from the beginning of the shift.
In the first shifting phase, the clutch actuator for actuating the power-shift clutch of the gearbox subunit which is connected into the driving connection in the middle gear can be filled or placed under an application pressure.
When the engine speed and thus the speed of the input shaft reaches the speed value of the middle gear during the increase in revs, it is possible with the present invention for a changeover in the actuation of the power-shift clutches to take place. The middle gear is engaged with reduced excitation of the power-shift clutch concerned without the steady rise in the speed of the input shaft being interrupted, with the result that no significant torque jumps at the output of the gearbox occur either.
When the speed of the input shaft has risen almost to the speed value of the new gear, the engine can be levelled off, i.e. the increase in the revs of the engine reduced.
When the filling of the clutch actuator for actuating the power-shift clutch of the gearbox subunit connected into the driving connection in both nonadjacent gears is complete, this being indicated by a pressure rise in the clutch actuator, it is possible, according to the present invention, for a crossover control to be triggered for the purpose of shifting to the new gear without an interruption to the tractive force.
In the case of shifts of multi-path toothed-wheel gear change boxes having loose wheels which can in each case be coupled to their shaft by a gearwheel clutch, it is customary, in a gearbox subunit in each case not connected into the driving connection between the input shaft and the output shaft, to, as it were, preselect the loose wheel of a gearwheel stage adjacent to the respectively selected gear as regards the transmission ration by engaging its associated gearwheel clutch.
In the case of a downshift via two nonadjacent gears in the method according to the invention, the gearwheel stage of the middle gear is engaged.
With a downshift via two nonadjacent gears in the method according to the invention, the gearwheel clutch of the gearwheel stage of the lower of the two nonadjacent gears is engaged.
With an upshift via two gears which are nonadjacent in terms of their transmission ratio in the method according to the invention, measures are first taken as a preparation for a shift to the middle gear. A subsequent engagement of the middle gear without an interruption to the tractive force then takes place in accordance with the crossover control.
When the power-shift clutch of the middle gear is capable of transmitting the torque of the input shaft on its own, the other power-shift clutch or the associated working pressure of the latter is disconnected completely, with the result that the middle gear can be engaged and the torque fed in to a level which is sufficiently high above the torque value associated with the middle gear for the engine or its speed to be steadily retarded.
In preparation for an engagement of the higher of the two nonadjacent gears in the method according to the present invention, a clutch-control signal for filling the power-shift clutch associated with the higher gear or the clutch actuator concerned is produced in the third shifting phase. This is followed by a shift from the middle to the higher gear without an interruption to the tractive force while the characteristic of the engine speed continues to fall steadily.
In a following shifting phase, the engine continues to be steadily retarded in its speed. The upshift via two nonadjacent gear is ended when the engine speed has fallen to the speed value corresponding to the higher gear.
With an upshift via two nonadjacent gears in the method according to the present invention, the gearwheel clutch of the gearwheel stage of the middle gear can be actuated o controlled and the gearwheel clutch of the gearwheel stage of the higher gear actuated or controlled.
In the case of an upshift via two nonadjacent gears, the clutch-control signal for the beginning of filling of the power-shift clutch or of the clutch actuator of the higher gear in the third shifting phase can be produced.